Can lux be converted to meters (of throw)?

[HighLumens]

After reading on Ra Lights' website the paragraph "How far can I see with my light", I started understanding something about throw and so on. Now I'd like to ask: is there a way to convert lux to meters of throw? Let's assume we are in total darkness: how far, for example, could I see with a flashlight putting out 3000 lux at 1 meter?

Please, I'd like a general formula to be able to convert every lux number into meters.

Thanks.

 

[Saint_Dogbert]

No, because a single lux measurement at a given distance does not account for beam angle. By beam angle, I'm talking about the central hotspot-producing part of the beam and how much it diverges with distance. Two lights with the same lux reading at 1 meter could have different beam angles, and thus very different amounts of throw. 3000 lux at 1m only tells you about illuminance at 1m. You have no way of knowing how the light will perform at longer distances like 50m or 100m.

If you do know the beam angle you could probably do some math to calculate lux at various distances from a singe known value. You'd need the inverse-square law and some basic trig knowledge for that. Hopefully someone smarter than me can furnish you with that info.

 

[mudman cj]

If lux measurements are taken at greater distances from the light, then the light source begins to approximate a point source and the intensity will conform to the inverse square law. Then, the throw can be estimated from the lux. The standard often used on CPF is to use the square root of the lux at 1 meter. This effectively determines the distance at which the light intensity would equal 1 lux.

I want to emphasize that readings taken at 1 meter may skew the results due to deviations from the inverse square law caused by things such as reflectors, especially 'large' ones. The best practice is to take lux measurements at greater distances, include only those that are apparently not skewed, and convert the readings to an equivalent value at 1 meter. I posted a thread on the topic if you would like details.

It seems that throw specifications given by manufacturers tend to exceed those calculated using this method, and in practice many people would find that they could use the light at greater distances than this approximation suggests. It seems that the arbitrary, but convenient, standard of 1 lux may be a little higher than necessary.

 

[Dioni]

Meters? absolutaly not. How would a high lux light behave in a dense fog night? the throw wont answer it!

 

[HighLumens]

Meters? absolutaly not. How would a high lux light behave in a dense fog night? the throw wont answer it!

I forgot to say that it should be an ideal scenario, so total darkness (as I said) and no fog of course.
Thanks for all the replies, I hadn' t thought about the beam angle at all, now it's so obvious :thumbsup:.

 

[Dioni]

I forgot to say that it should be an ideal scenario, so total darkness (as I said) and no fog of course.
Thanks for all the replies, I hadn' t thought about the beam angle at all, now it's so obvious :thumbsup:.

Haha.. only to complicate! But yet, it also depends on the color of the stuff you are lighting up. AFAIK the lux readings are get from a "white" wall.

 

[LEDninja]

You get 1 lux at square-root(measured lux at 1 meter) meters. That distance is used by flashlightreviews as throw.

http://www.flashlightreviews.com/features/lux.htm

 

[Ragiska]

yes, you can convert a lux measure into the official definition of throw (beam distance), as defined in ANSI/NEMA FL 1-2009 Flashlight Basic Performance Standard, sections 1.2.1 and 2.2.